The present invention relates to electric watthour meters and, more particularly, to techniques for improving the accuracy of measurement of electric watthour meters.
Electric watthour meters multiply a line voltage and load current to produce a quantity related to instantaneous power usage. The instantaneous power usage is integrated over time to accumulate energy consumed.
For many years, power usage was measured by rotation of a disk under the influence of magnetic fluxes and eddy currents produced by current and voltage stators. Integration was performed by coupling the rotation of the disk to a dial-type or cyclometer-type register.
In some watthour meters, measurement of a predetermined quantum of electric energy is denoted by the generation of a pulse. The pulses are accumulated over time to produce a measurement of the total amount of energy consumed. Such pulse-generating watthour devices are disclosed, for example, in U.S. Pat. Nos. 3,947,763 and 3,955,138.
All commercially acceptable watthour meters are required to maintain an accurate measurement of power usage over an extremely wide dynamic range. For example, a watthour meter rated at 30 amperes must continue to register with acceptable accuracy at 200 amperes and 3 amperes. Thus, a dynamic range of 66.7 (minimum to maximum) is required.
It is desired to increase the dynamic range over which acceptable metering accuracy may be maintained. A combination of electronic watthour metering using, for example, the techniques in the referenced patents, together with the teachings of the present disclosure, may provide such increased dynamic range.